1. Field of the Invention
The present invention relates to hard disk drives. More particularly, the invention relates to a method and apparatus adapted to drive a voice coil motor in a HDD to unload a read/write head.
This application claims the benefit of Korean Patent Application No. 10-2005-0123159, filed on Dec. 14, 2005, the subject matter of which is hereby incorporated by reference.
2. Description of the Related Art
A hard disk drive (HDD) is a well known recording device used within many host devices and applications to store data. Information is typically recorded on concentric tracks of a magnetic disk housed within the HDD. The disk is mounted on and rotated by a spindle motor. As the disk rotates, data is accessed (e.g., written to and/or read from) on the HDD by positioning one or more read/write head(s). The head is commonly mounted to an actuator arm which is positioned using a voice coil motor (VCM). In conventional HDDs, a VCM rotates an actuator arm in response to an applied VCM driving current. In this manner, the head is across the disk and precisely positioned to access desired data.
The head reads data recorded upon the surface of the disk by sensing variations in a magnetic field defined by the electro-magnetic properties of the disk's surface. To record (or write) data on the disk, a write current is supplied to the head. In response to the applied write current, the head generates a magnetic field which may be used to selectively define (or re-define) the electromagnetic properties of the disk's surface. For example, data recorded on the disk may vary in its nature according to a magnetization property imparted to a selected portion of the surface of the disk.
Movement and positioning of the head is critical to the proper operation of the HDD. When not being used, the head is commonly “parked” in a position where it may safely rest. The process of positioning and parking the head within the HDD when no tin use is generally referred to as “unloading” the head. Unloading operations may vary is their respective natures, but all unloading operations effectively park the head.
The parking location for the head is commonly referred to as “the ramp”. The term “ramp” has a historical basis wherein many early (as well as contemporary) parking locations for head are literally ramp structures. However, the term “ramp” should be broadly interrupted to denote any structure and related positioning adapted to receive an HDD head during an unloading operation. A head may be unloaded, for example, when power is interrupted to the HDD, when entering a power saving mode, when the HDD becomes idle, as the HDD is being turned OFF, or in circumstances where it is necessary to protect the head and/or the disk from an externally applied shock. For example, the HDD make detect a free-fall state and unload its head in anticipation of an impact as host device incorporating the HDD is dropped.
FIG. 1 is a schematic plan view of a conventional HDD 100 using one type of ramp structure. Referring to FIG. 1, HDD 100 includes at least one disk 12 rotated by a spindle motor 14. HDD 100 also includes at least one head 16 positioned relative to the surface of disk 12. Head 16 may read data from or write data to disk 12 as it rotates by sensing a magnetic field formed on the surface of disk 12 or by magnetizing the surface of disk 12. (For the sake of clarity only a single head will be described hereafter, bearing in mind that multiple read/write heads may be alternately used. For example, the single head 16 shown in FIG. 1 may comprise a write head for magnetizing disk 12 and a separate read head for sensing a magnetic field of the disk 12).
Head 16 may be assembled on a slider (not shown). The slider generates an air bearing between head 16 and the surface of disk 12. The slider may be combined with a suspension 20. Suspension 20 may be combined with a head stack assembly (HSA) 22. HSA 22 is attached to a VCM 30 through a mold structure 24 fixing a voice coil 26. Voice coil 26 is located adjacent to a magnetic assembly 28 specifying (supporting) VCM 30 together with voice coil 26. A VCM driving current supplied to voice coil 26 generates a driving force which rotates HSA 22 around a bearing assembly 32. The rotation of HSA 22 moves head 16 across the surface of disk 12.
When HDD 100 illustrated in FIG. 1 performs a head unloading operation, head 16 is positioned on a ramp 6 installed to the side of the outer circumference of disk 12.
FIG. 2 is a view for describing a conventional head unloading operation in relation to ramp 6. Referring to FIG. 2, when the head unloading operation is performed, head 16 is unloaded onto ramp 6 from disk 12.
FIG. 3 is a cross-sectional view of ramp 6 of FIG. 2. Ramp 6 has a cross section of a ladder shape and includes a first incline 6d, a flat surface 6c, a second incline 6b, and a safety zone 6a. Referring to FIG. 3, when the head unloading operation is performed, head 16 rises along first incline 6d until it lands within safety zone 6a. In actual practice, a projection 20a extending from suspension 20 to which head 16 is attached typically makes contact with ramp 6 when head 16 is positioned in safety zone 6a. 
To ensure reliable execution of the head unloading operation, the mechanical driving force provided by VCM 30 must be sufficient to safely land head 16 on ramp 6. If the driving force provided by VCM 30 is not sufficient, head 16 will not be able to rise over first incline 6d and reach the safety zone 6a. In such circumstances, heed 16 lands may come to rest on disk 12, thereby damaging head 16 and/or disk 12.
Conventionally, this potential problem has been addressed by increasing the driving force of VCM 30 by some margin that ensures reliable execution of the head unloading operation. This increase in driving force may be accomplished by increasing a torque constant associated with VCM 30 and/or increasing the driving current applied to VCM 30.
However, increasing the torque constant for VCM 30 also tends to increase its overall size (generally its height profile). This outcome is not desirable in view of ongoing attempts to reduce the size of HDD 100.
In addition, if the driving current applied to VCM 30 is increased, the driving force imparted by VCM 30 will generally increase as well. This outcome may result in an excessively high rate of movement for head 16. If head 16 moves at too high a speed, mechanical vibrations may arise the negatively influence operation of head 16 and may damage disk 12.